This research focuses internal process of product development until designers or development teams obtain design solution, and improve and develop the methodologies so called design rationale finding out its rational trajectory. The following results were obtained.(1) Categorization of contents of discussions:Concerning the record format as a basis of design rationale, its discussion part was categorized in accordance with its time, content and authorization level in order to make easy finding potential problems in past and ongoing project. In particular modification of content category was further classified into four types.(2) Development of transition pattern diagramTransition pattern diagram was developed as a tool to detect the potential problems based on the above well structured record format.(3) Implementation of support softwareIn order to implement computerized record and analysis, self hand software of IDEF3 was customized utilizing its evaluation function for the record format and PFD and OSTN for the transition pattern diagram respectively.The validity and effectiveness of the above proposals and implementation were verified through the data of rather large scale real software development case.